feat(tagless component) popperClass is now class and id is passed to attachment

[kybishop]

Implements #41
Paves the way for #37

I'm really happy with the changes introduced here:

1. We can now pass class and id directly to the popper element
2. No more ghost element where the {{ember-attacher}} was declared
3. Much cleaner tests now that we don't rely on didInsertElement
4. Greatly simplified internals now that we grab target from ember-popper instead of recalculating it ourselves